In this paper, a numerical method is used to predict the response of an elastic body during a collision in which both normal and tangential impulses are important. Results are compared with those from simplified prediction procedures, which stem from the assumptions that the energy-returning capacity of the normal deformation mechanism is constant and the tangential compliance is neglected. The finite-element predictions indicate the importance of the tangential compliance for elastic collisions wherein friction forces are significant. The results of both methods of prediction point up the roles of friction and inertia coupling in determining the normal velocity ratio (the "coefficient of restitution"). / Graduation date: 1992

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 139-143). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 139-143). Also available on the Internet.

The scattering of H2 from Si(100) has been studied using pulsed molecular beam techniques and quantum state-specific detection methods. These studies can be used to test theoretical calculations and give insight into new theories of molecule-surface interactions, a fundamental study in a diverse field of science and technology. In this work, time-of-flight (TOF) spectra of the elastic scattering of H2(v=1. J=1) and H2(v=0, J=1) from clean Si were recorded over a wide range of surface temperatures. Two data processing strategies were developed to extract rich kinematic information from the scattering experiments, e.g., mean translational energy exchange, absolutely survival probability, and angular and speed distribution of the scattered molecules. No such set of quantitative results has been reported before for this system. Compared with close packed metal surfaces, these scattering experiments from a covalently bonded semiconductor surface showed a completely distinct dynamics, e.g. the finding of energy gain instead of loss from the substrate, much broader angular distribution and some counterintuitive surface temperature effects. From the studies of molecules/surface scattering experiments, the thermal excitation on Si(100) surface which depends on surface temperature can substantially alter the adsorption barrier and its distribution, and therefore changes the kinematics of scattered molecules. As a result, even the most basic understanding of the dynamics has to include phonon excitation and deexcitation of the silicon substrate. / text

Angular distributions have been measured for the (⁹Be, ¹⁰B₀, ₁) reactions on ⁶³Cu, ⁵⁴Fe, ^26,24Mg and ¹⁶O at 43 MeV and on ⁴⁰Ca at 45 and 30 MeV. Several of these experiments were performed with the Oxford MDM-2 spectrometer and the design and testing of its 30 cm focal plane detector, which is of the "hybrid" type, is described. Despite the size of the counter, in particular the large cathode to Frisch-grid separation, the resolution of the ionization signals is comparable with that of smaller counters. The position resolution is < 0.6 mm. Optical potentials have been obtained from the measured elastic scattering of ⁹Be from ¹⁶O, ²⁶Mg and ⁴⁰Ca, and ¹⁰B from ²⁵Mg and ³⁹K. The exact finite-range DWBA calculations have generally well reproduced the shape of the experimental reaction cross-sections. However, inconsistencies of up to 50% between the extracted spectroscopic factors for ¹⁰B₀ and ¹⁰B₁ have been found. This anomaly was found insensitive to changes in either optical potential or bound state parameters. A new method of form factor calculation is described that uses a shell model potential in conjunction with a surface-peaked potential, the depth of which is adjusted to give the correct asymptotic form to the wavef unctions. Whilst this form factor showed some success, it did not account for the ¹⁰B₀/¹⁰B₁ anomaly. Collective model DWBA analyses of the inelastic excitation of the first 2⁺ state in ²⁶Mg and 3^- state in ⁴⁰Ca have given values for deformation parameters in reasonable agreement with light-ion work. A CCBA analysis of the ²⁶Mg 2⁺ state was carried out to estimate the effect of the coupling. Calculations performed for a two-step reaction process through inelastic excitation of a strongly coupled 5/2^- state in the projectile showed that this indirect route is important, but it could not solve the ¹⁰B₀/¹⁰B₁ problem alone. The conclusion is that other routes (projectile or target excitation) must be included.

Thesis (M.S. in Phys.)--Naval Postgraduate School, 1970. / Bibliography: l. 65-66. Also available online.

Made available in DSpace on 2014-10-09T12:50:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:42Z (GMT). No. of bitstreams: 1 00768.pdf: 4150056 bytes, checksum: 8e8c0f1f3b65b77306c6aeb1ee8f3508 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

Nesta tese de doutoramento foram propostos dois modelos teóricos (ZPM e GFA) para a obtenção da seção de choque de fusão e um (ZPM) para o cálculo do potencial de polarização para o canal elástico e correspondente seção de choque de espalhamento. Foi usado em todos os cálculos deste trabalho, tanto no tratamento da fusão quanto no do espalhamento elástico, o Potencial de São Paulo (SP), que possui como uma das principais características a total ausência de parâmetros ajustáveis. Conseqüentemente, todos os cálculos apresentados no contexto de diferentes modelos constituem previsões teóricas ao invés de simples ajustes de dados. Em uma análise comparativa acerca dos cálculos para a fusão, os modelos GFA e ZPM se mostraram equivalentes e compatíveis com cálculos de canais acoplados usuais, com a vantagem de incorporarem acoplamentos à toda banda vibracional e de permitirem a obtenção de cálculos acurados de seções de choque de fusão em energias extremamente abaixo da barreira. Aplicamos o modelo de ZPM ao cálculo da função de excitação de fusão para 112 sistemas de íons pesados, envolvendo tanto núcleos par-par como núcleos ímpar-par e ímpar-ímpar (incluindo alguns núcleos fracamente ligados), e confrontamos os resultados obtidos com dados experimentais existentes na literatura. Enquanto o modelo de penetração de barreira não-deformado prevê discordâncias de até onze ordens de magnitude, as previsões do modelo de ZPM mostraram-se de acordo com os dados dentro de duas ordens de grandeza. Ao confrontarmos os resultados do modelo de ZPM para as seções de choque de espalhamento elástico com dados experimentais para alguns sistemas em energias em torno da barreira coulombiana, pudemos constatar uma boa concordância. Desta forma, demonstramos que é possível tratar os canais de espalhamento elástico e de fusão de maneira consistente dentro do mesmo contexto. / In this Ph.D. thesis two theoretical models (ZPM and GFA) were proposed in order to obtain fusion cross sections and one (ZPM) to calculate the polarization potential for the elastic channel and the corresponding scattering cross section. The São Paulo (SP) potential, which has as one of its main characteristics the complete absence of adjustable parameters, was used as bare interaction in the calculations of the present work. Therefore, all results, presented in the context of different models, correspond to theoretical predictions instead of simply data fit. After a comparative analysis of fusion calculations, the GFA and ZPM models demonstrated to be equivalents and compatible with the usual coupled channel calculations, with the advantage of incorporating inelastic couplings to the complete vibrational band and of providing accurate fusion cross sections at extreme low energies relative to the Coulomb barrier. We applied the ZPM model to the calculation of the fusion excitation function for 112 heavy-ion systems, involving not only even-even nuclei but also odd-even and odd-odd ones (including some weakly-bound nuclei), and we compared the theoretical results with experimental data existing in literature. While the usual non-deformed barrier penetration model provides enhancements up to eleven orders of magnitude, the ZPM model predictions are in good agreement with the data within only two orders of magnitude. When confronting the ZPM model results with experimental data of elastic scattering cross sections for some systems, at energies around the Coulomb barrier, we found out good agreement between them. Therefore, we demonstrated that it is possible to treat the elastic scattering and fusion channels in a consistent manner, within the same context.

Radioactive beams of 8Li and 6He were produced using the double superconducting solenoid system of RIBRAS (Radioactive Ion Beams in Brasil) with a primary beam of 7Li of Elab = 30 MeV, at the São Paulo Pelletron Accelerator. The production reactions were 9Be(7Li, 8Li)8Be and 9Be(7Li, 6He)10B. The angular distributions of the elastic scattering of the 8Li radioactive beam of 26.0 MeV and 6He radioactive beam of 23.0 MeV were measured on 51V target of 1.9 mg/cm2.The elastic scattering angular distributions were analyzed using Optical Model, where the real and imaginary parts are described through a Non-Local Interaction Model called São Paulo Potential . The results were compared with the data present in the literature. The largest cross section, particularly for the halo 6He, shows evidence of the importance of the break up for these medium mass systems. [1]R. Lichtenthaler et al, Eur. Phys. J. A 25,s01,733 (2005); [2]L.C. Chamon et al, Phys. Rev. C66 (2002) 014610. / Radioactive beams of 8Li and 6He were produced using the double superconducting solenoid system of RIBRAS (Radioactive Ion Beams in Brasil) with a primary beam of 7Li of Elab = 30 MeV, at the São Paulo Pelletron Accelerator. The production reactions were 9Be(7Li, 8Li)8Be and 9Be(7Li, 6He)10B. The angular distributions of the elastic scattering of the 8Li radioactive beam of 26.0 MeV and 6He radioactive beam of 23.0 MeV were measured on 51V target of 1.9 mg/cm2.The elastic scattering angular distributions were analyzed using Optical Model, where the real and imaginary parts are described through a Non-Local Interaction Model called São Paulo Potential . The results were compared with the data present in the literature. The largest cross section, particularly for the halo 6He, shows evidence of the importance of the break up for these medium mass systems. [1]R. Lichtenthaler et al, Eur. Phys. J. A 25,s01,733 (2005); [2]L.C. Chamon et al, Phys. Rev. C66 (2002) 014610.

Nesse trabalho medimos e analisamos distribuições angulares do espalhamento elástico para os isótopos 7Be, 9Be e 10Be em alvo de 12C. A distribuição do 7Be foi medida a uma energia de 18.8 MeV, em dois laboratórios, com o sistema TWINSOL, na Universidade de Notre dame, e com o sistema RIBRAS, na Universidade de São Paulo, onde foi completada a distribuição angular. As distribuições para o 9Be e 10Be foram medidas completamente no sistema RIBRAS, em energias de 26.0 e 23.2 MeV, respectivamente. Cada uma dessas distribuições angulares foi analisada considerando no modelo ótico e também o formalismo dos canais acoplados. Testamos múltiplos potenciais óticos em cada distribui9ção, com a finalidade de descrever a seção de choque elástica de cada sistema. Para os sistemas que envolvem núcleos fracamente ligados (7Be, 9Be e 8B) foram feitos cálculos com acoplamento do contínuo (CDCC), enquanto que para o núcleo 10Be, que é fortemente ligado, acoplamos os dois primeiros estados ligados. Também, a partir da análise de cada uma das distribuições elásticas, foi possível obter a seção total de reação, que foi comparada sistematicamente com outros núcleos leves espalhados em carbono. Dessa análise foi possível concluir que o canal do break up Coulombiano, nesses sistemas leves, não é fortemente influente na seção de choque total de reação, o que implica que a interação entre alvo e projétil é dominada pelo potencial nuclear. / In the present work, we measured elastic scattering angular distributions for teh isotopes 7Be, 9Be and 10Be on 12C target. The angular distribution of 7Be at 18.8 MeV, was measured in two laboratories, with the TWINSOL system, in Notre Dame University, and the RIBRAS system, in São Paulo University, where the angular distribution was completed. The angular distribution for 9Be and 10Be isotopes measured completely in the RIBRAS system at 26.0 and 23.2 MeV, respectively. All angular distribution were analized considering optical model and coupled channel formalism. We tested multiple optical potentials on each distribution to describe the elastic cross section for these systems. For the weakly bound projectiles (7Be, 9Be and 8B)calculations with continous coupling (CDCC) were performed, while for the 10Be nucleus, which is tghtly bound nucleus, we coupled the first two bound states. We also performed a systematic analysis of the total reaction cross section obtained from elastic scattering distribution of several light particles on 12C. From this analysis, we concluded that the Coulomb break up channel, in these light systems, does not have a strong influence on the total reaction cross section, what implies that the projetile-target interaction is dominated by the nuclear potential.